This invention relates to wire matrix print head assemblies and, more particularly, to new and improved guide and bearing apparatus for enabling assembly of wire print members by continuous uninterrupted axial movement relative to the guide and bearing apparatus and for enabling accurate reliable reciprocable operation after assembly of the wire print members on accurately located and positioned multiple bearing means portions of the guide and bearing apparatus with the print end portions of the wire members arranged in accurate relatively closely spaced juxtaposition.
In general, the bearing apparatus of prior wire matrix print head assemblies of the type disclosed in my prior U.S. Pat. Nos. 3,939,214, 3,994,381 and 4,051,941 has comprised a pair of axially spaced relatively narrow width intermediate wire support members located in widely axially spaced relationship between an armature end passage and a print end passage in a wire housing portion of the assembly. The assembly of the wire members during manufacture of such print head assemblies and the removal and replacement of wire members for service, maintenance and repair has been tedious, costly and time consuming due to the fact that the wire members have a bowed configuration in the assembled position requiring manual alignment from passage to passage to enable insertion in each of the individual wire passages including not only the intermediate passages but also the print end bearing passage which is conventionally an expensive and fragile ruby or ceramic bearing member requiring careful costly placement relative to the intermediate passages. Furthermore, the wire members must be individually inserted in a predetermined sequence and, consequently, also removed in a predetermined sequence so that repair and replacement of a particular wire member usually also requires removal of additional wire members. The conventional assembly procedure involves the use of special thin tweezers to grip and locate the end of the wire members relative to and prior to being received in each passage after the first armature end passage resulting in interrupted, discontinuous axial movement of the wire members.
One prior attempt to solve these problems has involved the use of a continuous straw-like tube for each wire member having a constant diameter substantially in excess of the diameter of the wire member with the tube being mounted in a flexible bowed condition between the end passages. Among the various problems associated with such a tube are that the axial spacing and location of the intermediate bearing portions, which is critical to performance, cannot be adequately maintained; adequate circumferential bearing support of the wire members at the critical locations cannot be maintained; and the tubular passage tends to create a capillary action during reciprocating movement of the wire members causing flow of ink into the passage whereby the ink in the passage impedes the continued satisfactory performance of the apparatus.
In general, the present invention involves the provision and use of relatively low cost, easily assembled, durable wire bearing means in a wire matrix print head assembly which enables assembly of the wire members by continuous uninterrupted axially directed assembly movement while also providing for accurate bearing support of the wire members at proper positions and locations therealong in the assembled position resulting in improved performance in use. In the presently preferred embodiment, the bearing means comprises two elongated interconnectable separate bearing members, each being made of one piece of molded plastic material having a plurality of axially aligned wire passages which, upon assembly and interconnection of the separate bearing members, provide relatively short length accurately axially spaced bearing means passage portions in a continuous elongated wire guide passage enabling assembly insertion of the wire members by continuous uninterrupted axial movement therealong.
The construction and arrangement of each wire passage is such as to provide a first relatively long length guide means passage portion next adjacent the drive end portion of the wire member which is of enlarged cross-section relative to the diameter of the wire member to enable a first intermediate portion of the wire member to be received therein in a bowed condition and operated therein without restrictive engagement with the side wall of the guide passage portion. A first relatively short length bearing means passage portion is provided at the end of the first guide means passage portion and has a circular cross-section of a diameter slightly larger than the diameter of the wire member to enable free slidable reciprocating movement of the wire member therein while providing circumferentially confining bearing support for a relatively short length intermediate portion of the wire member and also serving to reduce the degree of curvature and change the direction of the wire member. A second relatively long length guide passage means portion is located next adjacent the first bearing means passage portion and has an enlarged cross-section relative to the diameter of the wire member to enable a second relatively long length intermediate portion of the wire member beyond the first bearing means passage portion to be received therein in a lesser bowed condition than the drive end portion of the wire member and operated therein without restrictive engagement with the side wall thereof. A second bearing means passage portion of relatively short length is located next adjacent the second guide passage means and has a cross-section slightly larger than the diameter of the wire member to enable slidable reciprocating movement of the wire member therein while providing confining bearing support for a second relatively short length intermediate portion of the wire member and also serving to reduce the degree of curvature of the second relatively long length intermediate wire portion and change the direction of the wire member from curvilinear to substantially linear. A third relatively long length guide means passage portion is located next adjacent the second bearing means portion, and has an enlarged cross-section relative to the diameter of the wire to enable a third relatively long length intermediate portion of the wire member beyond the second bearing means passage portion to be received therein in an inwardly inclined condition and operated therein without restrictive engagement with the side wall thereof. A third relatively short length terminal bearing means passage portion is located next adjacent the third guide passage portion and has a diameter slightly larger than the diameter of the wire member to enable free sliding reciprocating movement of the print end portion of the wire member therein while providing confining bearing support therefor limiting the reciprocable movement to a linear path with the linear paths of movement of each wire member being parallel.